Belt conveyors are used as means for conveying various packages such as materials, foods, etc. Recently, with growth in traffic volume and increase in transport efficiency, large-sized belt conveyors have become used, and those of which the overall length reaches a few km have come in use. Accordingly, higher durability is desired and reduction in power consumption is also desired.
The belt (conveyor belt) to be mounted to the belt conveyor generally has a core as a reinforcing member inside it, and the core is sandwiched between a cover rubber on the upside of the core (that is to be the outer periphery when used in a conveyor belt) [hereinafter referred to as an external cover rubber) and a cover rubber on the inner periphery (that is to be the back or the lower side, when used in a conveyor belt) [hereinafter referred to as internal cover rubber]. The external cover rubber and the internal cover rubber positioned on the back thereof differ in point of the necessary physical properties, and the internal cover rubber must have tear resistance, and furthermore, must reduce the energy loss owing to contact between the conveyor belt and a large number or rollers, or that is, must reduce the amount of power consumption through energy loss reduction.
Heretofore, as a rubber composition for conveyor belts excellent in tear resistance, there are known a rubber composition that comprises natural rubber (NR) and, as incorporated thereinto, butadiene rubber (BR) and styrene-butadiene rubber (SBR) in a different combination, etc. (see Patent document 1 and 2).